Roof, 22, suffered bruising around his face and on his back after being struck with a fist, Charleston County Sheriff Al Cannon said at a press conference. He was not seriously injured and there were no weapons involved, according to officials.

Roof and his attorneys will not be pressing charges against the inmate, Dwayne Stafford, Cannon said.

Authorities are investigating how Stafford, who is being held at the Cannon Detention Center on a strong armed robbery charge, was able to exit his locked cell door and approach Roof as he was about to take a shower at approximately 7:45 a.m., Cannon said.

Officers had checked if the cells in the area were locked before letting Roof out of his cell to take a shower, Cannon told reporters. However, Stafford left his cell, ran down the stairs, and began assaulting Roof with his hands. Detention officers broke up the altercation, Cannon said.

"We are looking at the issue of the door lock and what may have failed there," Cannon said at the conference, adding that jail employees were also being interviewed.

He said that although Roof was always accompanied by detention officers, one officer was dropping off toilet paper, and another was taking a break — an uncommon procedure when an inmate is taking a shower — when the incident occurred.

"This serves as a wake-up call," Cannon said. "Up and down the chain, we have to ensure that our folks do not fall prey to the routine."

Tasneem Nashrulla is a reporter for BuzzFeed News and is based in New York.